Time-Division Multiplexing (TDM) is a type of digital multiplexing in which two or more signals or bit streams are transferred simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel. The time domain is divided into several recurrent timeslots of fixed length, one for each sub-channel. After the last sub-channel, the cycle starts all over again.
TDM is commonly used for circuit mode communication with a fixed number of channels and constant bandwidth per channel. Time-division multiplexing differs from statistical multiplexing, such as packet switching, in that that the timeslots are recurrent in a fixed order and pre-allocated to the channels, rather than scheduled on a packet-by-packet basis.